Abdullah told a rally of thousands of rowdy supporters in Kabul he would fight on to win the presidency, but he called for patience from loyalists who demanded he declare a “parallel government” to rule the country.

“We are proud, we respect the votes of the people, we were the winner,” Abdullah said. “Without any doubt or hesitation, we will not accept a fraudulent result, not today, not tomorrow, never.”

Before he spoke, a huge photograph of President Hamid Karzai was ripped down from the stage — underlining the boiling anger among Abdullah’s supporters after the preliminary result in favour of poll rival Ashraf Ghani.

The election stand-off has sparked concern that protests could spiral into ethnic violence and even lead to a return to the fighting between warlords that ravaged Afghanistan during the 1992-1996 civil war.

Meanhwile, the United States warned on Tuesday it would withdraw financial and security support from Afghanistan if anyone tried to take power illegally, as supporters of a presidential candidate rallied in Kabul for a parallel government. In a sharp warning, Kerry said there was no justification for violence or “extra-constitutional measures”.

“I have noted reports of protests in Afghanistan and of suggestions of a ‘parallel government’ with the gravest concern,” he said in a statement issued by the US embassy in Kabul.